When transmitting radiant energy, such as radar, to determine the range and velocity of an object, it is important to have consistent center frequency and bandwidth in order to accurately determine the exact range and velocity of the object.
Range errors occur when the bandwidth of the modulated signal varies, resulting in unreliable ranging capability. When the ranging capabilities are part of an anticipatory collision detection system to determine whether a collision with an object will occur, it is critical to consistently and accurately determine the range of the object. If the bandwidth changes, the range to the object will be inaccurate and produce a poor range resolution. For example, if the bandwidth decreases, the object will appear to be closer. In the case of a collision detection system, that means a signal to activate the passenger restraint system may occur too early, perhaps unnecessarily, if no collision occurs. If the bandwidth increases, the object will appear farther than it is and the system will activate too late or not at all. In order to determine when, if at all, a collision will occur, it is also imperative that the velocity as well as the range be determined accurately and quickly. If the frequency of the modulated signal increases or decreases, the velocity calculation will be inaccurate.
Not only must the frequency and bandwidth be determined accurately in the case of an anticipatory collision detection system for a passenger restraint system in an automobile, but it is important as well that the center frequency and bandwidth be adjusted instantaneously. This is due to the narrow window of time available to the collision detection system to determine whether a collision will occur, given the speed at which collisions often occur. If the frequency and bandwidth are not determined instantaneously, a collision may occur before the system can activate the passenger restraint system.
Accurate range and velocity determination is not the only reason for maintaining the center frequency and proper bandwidth. In order to stay within guidelines set by the FCC for unlicensed sensor operation at 5.8 GHz, proper frequency and bandwidth must be maintained.
Providing frequency and bandwidth control to an anticipatory collision detection system for a passenger restraint system for an automobile typically requires a substantial cost to manufacture and implement. It is important that the center frequency and bandwidth be maintained regardless of external influences such as temperature. However, in order to avoid temperature effects, expensive components must be used and considerable time must be spent in trimming and calibrating the components to perform in any environment. Alternatively, without such expensive components, calibration may take place after implementation in the automobile in order for proper operation in a particular environment. Neither option presents a cost effective means of manufacture or implementation.
It would therefore be advantageous to dynamically adjust the center frequency and bandwidth of a modulated signal quickly, regardless of external influences such as temperature, and provide such control while avoiding the need to trim and calibrate components during manufacture, or calibrate the components after implementation in an automobile.